In the related art, in a chemical plant or the like, a regulating valve is used for process control of a flow rate. A valve opening of the regulating valve is adjusted by a setting/operating device (hereinafter, also referred to as an “actuator”) that operates a valve stem of a regulating valve based on a control signal from a positioner.
In general, in the case of a rotary-type regulating valve, such as a butterfly valve, a valve member of the regulating valve may be opened and closed by a force of a fluid that is under control. For example, in a case of an electric actuator, when an electric supply to the actuator is stopped due to an interruption of electric service, or the like, within a plant, a retaining force for a drive motor in an interior of the actuator is lost and an opening degree of the regulating valve may not be maintained.
Therefore, a power transmitting mechanism that drives the valve stem of the actuator requires a self-lock function that prevents the valve stem from operating even when no electric power is supplied. As the power transmitting mechanism that realizes the self-lock function, as disclosed in PTL 1 and PTL 2 described below for example, a paradox planetary gear mechanism is well known. PTL 3 describes a setting/operating device in which the planetary gear mechanism is employed as a power transmitting mechanism for a valve stem.